A study of the magnetism of ancient rocks suggests that plate tectonics – the drifting of continents – may have started at least 3.2 billion years ago and could have played a part in the evolution of life.
“If plate tectonics happened on the early Earth, that means that these processes were likely playing a part in the evolution of life,” says Alec Brenner at Harvard University. The rich variety of life of Earth couldn’t exist without plate tectonics, which helps recycle key elements such as carbon and also maintains a relatively stable temperature. “In part, we have plate tectonics to thank for Earth being habitable,” says Brenner.
Previously, the earliest evidence for plate tectonics was around 2.8 billion years old. Now Brenner and Roger Fu and their colleagues have studied a 3.2-billion-year-old volcanic rock formation in Western Australia called the Honeyeater Basalt. They used a newly developed instrument called a quantum diamond microscope, which let them visualise the magnetic fields of the iron oxide mineral magnetite. The team looked at a series of rock samples formed over a period of about 180 million years. The magnetic signal within the magnetite was shaped by Earth’s magnetic field at the time the mineral formed. Changes in the direction of the magnetism in the rocks over the period suggest that they moved some 2.5 centimetres a year over the 180 million years.
That is similar to the speed at which the continents move today, says Brenner. “About 3.2 billion years ago, at least some of the Earth’s crust was moving fast enough to suggest that plate tectonics was driving that motion,” he says.
The team checked that the magnetic signal in the rock samples really is from the time that the rock originally formed instead of from a later event. Fu says he is confident that the signal is indeed pristine.
Brenner says it is possible that plate tectonics goes even further back. “We’re actively working on rocks from Australia and South Africa that are up to 3.5 billion years old – the hope is that we can probe for the presence or absence of tectonics even further back in time.”